U.S. patent number 4,922,512 [Application Number 07/360,608] was granted by the patent office on 1990-05-01 for isocentric x-ray equipment stand having four axes of rotation.
This patent grant is currently assigned to General Electric CGR SA. Invention is credited to Jean Caugant, Pierre Lajus.
United States Patent |
4,922,512 |
Lajus , et al. |
May 1, 1990 |
Isocentric x-ray equipment stand having four axes of rotation
Abstract
In an x-ray equipment stand designed to perform isocentric
scanning movements and having three axes of rotation concurrent to
the isocenter O, the isocenter can be caused to rotate about a
fourth axis (Axis 4) perpendicular to the second axis (Axis 2) and
parallel to the third axis (Axis 3). This permits displacement of
the isocenter in the horizontal plane, especially along straight
lines which are secant with the third axis.
Inventors: |
Lajus; Pierre (Meudon,
FR), Caugant; Jean (Chevilly Larue, FR) |
Assignee: |
General Electric CGR SA (Paris,
FR)
|
Family
ID: |
9366938 |
Appl.
No.: |
07/360,608 |
Filed: |
June 2, 1989 |
Foreign Application Priority Data
|
|
|
|
|
Jun 3, 1988 [FR] |
|
|
88 07442 |
|
Current U.S.
Class: |
378/197;
378/195 |
Current CPC
Class: |
A61B
6/4441 (20130101) |
Current International
Class: |
A61B
6/00 (20060101); H05G 001/02 () |
Field of
Search: |
;378/195,196,197,198 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Church; Craig E.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is claimed is:
1. An isocentric x-ray equipment stand, comprising:
an X-ray source;
an X-ray detector;
an arcuate member carrying said source and said detector wherein
said arcuate member defines an imaging chain axis which passes
through an isocenter, said arcuate member being displaceably
mounted for rotation about a first axis perpendicular to the plane
of said arcuate member and passing through the isocenter wherein
said arcuate member is also displaceably positioned for rotation
about a second axis in the plane of the arcuate member or in a
parallel plane perpendicular to said first axis and also passing
through said isocenter;
a rigid structure supporting said arcuate member wherein said rigid
structure is pivotably mounted about a third axis perpendicular to
said first and second axis and passing through said isocenter;
and
rotation means for causing said isocenter to rotate about a fourth
axis perpendicular to said second axis and parallel to said third
axis.
2. An isocentric x-ray equipment stand according to claim 1,
wherein the rigid structure has the shape of a circular arc, one
end of which is pivotally fixed on the ground and the other end of
which is adapted to support the arcuate member and its associated
means for rotation about the first and second axes as well as the
means for rotation of the isocenter about the fourth axis.
3. An X-ray equipment stand according to claim 2, wherein the rigid
structure has a first horizontal portion which rests and moves on
the ground while pivoting about the Axis 3 and a second vertical
portion which supports the arcuate member and its associated means
for rotation about the first and second axes as well as supporting
the means for rotation of the isocenter 0 about the fourth axis
(Axis 4).
4. An x-ray equipment stand according to claim 1, wherein means are
provided for allowing coordinated angular displacements about the
third axis (Axis 3) and fourth axis (Axis 4) so as to displace the
isocenter along a predetermined path in the horizontal plane which
passes through the isocenter.
5. An x-ray equipment stand according to claim 4, wherein said path
of displacement of the isocenter is a straight line which is secant
with the third axis and is obtained by an angular displacement
about the fourth axis which angular displacement is double the
angular displacement about the third axis.
6. An x-ray equipment stand according to claim 1, wherein the x-ray
detector is pivotally mounted for rotating about the axis RX of the
imaging chain so as to compensate for rotation of the image at the
time of angular movements about the third and fourth axes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to x-ray installations and, more particularly
in an installation of this type, to an x-ray equipment stand which
permits isocentric scanning or examination of a patient at multiple
angles of incidence.
2. Description of the Prior Art
X-ray examination of a patient is performed by means of an imaging
chain which, as a general rule, is essentially constituted by an
x-ray source, a collimator, an anti-diffusion grid and a receiver
which are carried in rigidly assembled relation by a structure
known as a stand.
The x-ray source and the collimator are located on the same side
with respect to the patient to be examined who is placed on a table
whilst the anti-diffusion grid and the receiver are on the opposite
side. A straight line passing through the focus of the x-ray source
and the center of the receiver represents the axis of x-radiation
or imaging chain axis. In the case of isocentric scanning or
examination, this axis always passes through the same point of a
zone to be scanned irrespective of the orientation of said axis and
this point constitutes the isocenter. The movement which makes it
possible to vary the orientation of the imaging chain axis with
respect to the isocenter is known as an isocentric movement.
Stands which serve to carry out an isocentric movement usually
consist of an open arch or arcuate member, one end of which carries
the x-ray source and the other end of which carries the receiver.
The axis of the imaging chain passes through the isocenter which
constitutes the center of the arcuate member or is located on the
same axis as the center of the arcuate member so that a first
isocentric movement is performed by rotating the arcuate member
about its center in its plane, for example by displacing the
arcuate member in sliding motion within a sleeve having the shape
of a circular arc.
X-ray equipment stands permit in addition a second isocentric
movement which consists of rotation of the plane of the arcuate
member about a second axis of rotation which is perpendicular to
the first and also passes through the isocenter.
In certain x-ray equipment stands, provision is made for a third
isocentric movement which consists of a rotation about a third axis
of rotation which is perpendicular to the plane of the first and
second axes and passes through the isocenter.
It is apparent that these three isocentric movements make it
possible to take pictures of the patient in incidence and in planes
which can be oriented in all directions in space.
In an x-ray installation, the patient is placed on a table which
permits displacements of the patient in three directions, namely
one direction in elevation (z-axis) and two directions in the
horizontal plane (x-axis in the longitudinal direction of the
patient and y-axis in the perpendicular direction). The aim of
these movements is to cause the isocenter to coincide with the
center of the zone to be examined.
An installation of this type is attended by a certain number of
disadvantages. One disadvantage lies in the fact that it is
cumbersome since it calls for the use of a patient support table
which moves in the horizontal plane so as to place the center of
the zone to be observed at the isocenter of the stand.
Another disadvantage is that the stand has considerable overhang
since it has to permit longitudinal displacement of the patient
over a substantial width. This also has the effect of increasing
the bulk of the installation.
SUMMARY OF THE INVENTION
One object of the present invention is therefore to construct an
isocentric x-ray equipment stand which makes it possible to take
pictures of the patient in incidence without any need to displace
the patient in order to cause the isocenter to coincide with the
center of the zone to be examined.
Another object of the present invention is to construct an
isocentric x-ray equipment stand which makes it possible to reduce
the bulk of the x-ray installation.
The invention relates to an isocentric x-ray equipment stand which
comprises an X-ray source and an x-ray detector carried by an
arcuate member and defining an imaging chain axis which passes
through an isocenter, said arcuate member being capable of
displacement in rotational motion about a first axis (Axis 1)
perpendicular to the plane of the arcuate member and passing
through the isocenter as well as about a second axis (Axis 2) in
the plane of the arcuate member perpendicular to the first axis and
also passing through the isocenter, said arcuate member being
supported by a rigid structure which pivots about a third axis
(Axis 3) perpendicular to the first and second axes and passing
through the isocenter.
The invention is distinguished by the fact that it includes
rotation means for causing the isocenter to rotate about a fourth
axis (Axis 4) perpendicular to the second axis and parallel to the
third axis.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view which shows diagrammatically the relative
positions of the different axes of rotation of an equipment stand
in accordance with the invention.
FIG. 2 is a geometrical drawing showing the rectilinear
displacement which can be obtained by means of two coordinated
angular movements.
FIG. 3 is a view in elevation showing one example of construction
of an equipment stand in accordance with the invention.
FIG. 4 is a view in isometric perspective showing an x-ray
installation which makes use of an isocentric equipment stand in
accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, which is a view showing diagrammatically the relative
positions of the different axes of rotation of an equipment stand
in accordance with the invention, there are shown the three
orthogonal axes x'x and y'y in the horizontal plane and z'z in the
vertical plane which are concurrent to a point 0. The stand
comprises an arcuate member 13 which supports an x-ray source 11
and a detector 12 placed along the diameter of the arcuate member.
Said arcuate member is supported by a sleeve or guide 14 within
which it is capable of sliding under the control of the operator. A
patient support table 15 or so-called examination table is placed
between the x-ray source 11 and the detector 12 in the longitudinal
direction x'x and slightly beneath the horizontal plane defined by
the axes x'x and y'y.
A displacement of the arcuate member 13 in sliding motion makes it
possible to carry out a rotation of the x-ray source and of the
detector about an axis 1 perpendicular to the plane which contains
these two elements, which means that the axis of the x-ray beam
describes a surface in a plane parallel to said plane. In the
particular case of FIG. 1, the Axis 1 coincides with the axis
y'y.
The sleeve 14 is capable of rotating about an Axis 2 located in a
horizontal plane which passes through the point 0 known as the
isocenter. In this particular case of FIG. 1, said Axis 2 coincides
with the axis x'x. As a result of rotation of the arcuate member 13
about the Axis 2, the axis of the x-ray beam can be caused to
describe a surface perpendicular to the plane of the arcuate
member.
The support of the Axis 2 (not shown in the drawings) is capable of
rotating about an Axis 3 which coincides with the vertical axis z'z
and therefore passes through the isocenter 0. This rotation about
the Axis 3 makes it possible to displace the arcuate member 13 on
each side of the examination table or in other words to provide
freedom of access to the patient's head.
These three rotations about the Axes 1, 2 and 3 serve to scan zones
of the patient's body at angles of incidence which have any
directions in space but which all pass through the isocenter 0. It
is accordingly apparent that, in order to examine another organ of
the patient's body, this latter or in other words the examination
table has to be displaced with a view to bringing the center of
this other organ to the isocenter 0.
In accordance with the invention, it is proposed to displace the
isocenter 0 so that this latter can be made to coincide with the
center of the zone of the patient to be observed by providing for
rotation of the Axis 2 about an Axis 4 which is perpendicular to
the Axis 2 and located in the plane containing the Axis 3 in the
case of the particular position of FIG. 1. This rotation about the
Axis 4 makes it possible to displace the isocenter 0 in the
horizontal plane defined by the axes x'x and y'y by causing it to
describe a circular arc. Since the Axis 4 is in any case capable of
rotating about the Axis 3, it is possible to cause the isocenter 0
to describe any curve in the horizontal plane by combining the two
angular movements about the Axes 3 and 4.
The geometrical diagram of FIG. 2 serves to gain an understanding
of the movements which can be performed by virtue of the presence
of said Axis 4. This diagram has been drawn in the horizontal plane
and the point A materializes the position of the isocenter as well
as that of the axis z'z or Axis 3. The Axis 4 is therefore capable
of moving on a circle 16 having a center A so as to cover
approximately an angle of 135.degree. on each side of the axis x'x
as it passes on the side corresponding to the patient's head. The
fact that the angle is limited to approximately 135.degree. on each
side is due to the presence of the examination table support on the
side corresponding to the patient's feet. In respect of each
position on said circle 16, the equipment stand has three
concurrent axes, thus permitting all angles of incidence about the
isocenter.
It may also be understood from FIG. 2, that, by virtue of the
combination of the angular movement about the Axis 3 and of the
angular movement of the Axis 2 about the Axis 4, the isocenter can
be made to describe the segment DB on the axis x'x and the segment
EC on the axis y'y. The law which associates the two angular
movements must be such that, when the Axis 4 rotates through an
angle .alpha. about the Axis 3, the Axis 2 must rotate through an
angle 2.alpha. about the Axis 4.
Thus, when the Axis 4 is in position N, that is to say on the axis
y'y, the isocenter is at the point A. If the Axis 4 rotates through
the angle .alpha. in order to move to position M, the isocenter
will be on x'x at the point D if the Axis 2 rotates through an
angle 2.alpha. about the Axis 4 in the direction 4 defined by the
arrow 21. In fact, the triangle defined by the points A, M and D
must always be isosceles with the side b equal to the distance
between axes of the equipment stand or in other words the distance
between the isocenter and the Axis 4. As a result, the vertex angle
must be equal to 2.alpha. if the angle MAN is equal to .alpha..
When the Axis 4 passes from N to P, the isocenter will describe the
segment AB if the Axis 2 rotates in the direction defined by the
arrow 22. It is understood that the isocenter can describe the
segments AB and AD when the Axis 4 describes respectively the
circular arcs N'M' and N'P'.
In order to ensure that the isocenter describes the segment EA, the
Axis 4 must describe the circular arc PQ whilst the Axis 2 must
rotate in the direction indicated by the arrow 23. In the case of
AC, the Axis 4 must describe the circular arc QM' whilst the Axis 2
must rotate in the direction of the arrow 24. It will be understood
that, in this case also, the isocenter can describe the segments AE
and AC when the Axis 4 describes the circular arcs Q'M and Q'P' but
this possibility is not put to use since the support of the
examination table prevents displacement over part of the circular
arc P'Q'M.
The length of the segments described by the isocenter on the axes
x'x and y'y is given by the formula
as determined by means of the trigonometric relations of the
isosceles triangle DMA, for example.
The principles demonstrated in the foregoing in regard to
displacement of the isocenter on the axes x'x and y'y can be
demonstrated in the case of any other system of orthogonal axes
which is inclined with respect to the axes x'x/y'y. This shows that
the isocenter can be displaced to any point of the horizontal plane
defined by x'x and y'y but within a circle having a radius 2b sin
.alpha. and having a center A.
It is worthy of note that the radius of this circle is limited by
the maximum value which can be assumed by the angle .alpha., taking
into account the presence of the examination table.
When the isocenter describes the segments AD, AB, AE and AC, the
x-ray beam follows the angular movement about the Axis 3 and
rotates through an angle .alpha.. As a result, the image received
by the detector also rotates and corrections therefore have to be
made in order to ensure that it retains the same orientation in
space. These corrections can be obtained by making use of
electronic means and/or methods for producing action on the image
itself or by making use of means for producing action directly on
the orientation of the detector as a function of the value of the
angle .alpha..
FIG. 3 is a view in elevation of one example of construction of an
equipment stand for carrying out the invention described with
reference to FIGS. 1 and 2. In FIG. 3, the elements which are
identical with those of FIG. 1 are designated by the same
references. The sleeve 14 is carried by an element 16 and this
latter carries the rotating shaft which materializes the Axis 2.
Said shaft is capable of rotating through an angle of plus or minus
180.degree., which means that the arcuate member is capable of
performing one complete revolution about the Axis 2. The element 16
is carried at the upper end of a rigid structure 17 having the
shape of a circular arc, the lower end of which is capable of
pivoting about the Axis 3 between -135.degree. and +135.degree..
This Axis 3 is materialized by a shaft which is fixed on the ground
18 by means of a base 19. In accordance with the invention, the
element 16 is mounted for pivotal displacement about the Axis 4
which is vertically mounted at the upper end of the pivoting
structure 17. The angular movement is limited between the positions
-90.degree. and +90.degree..
The detector 12 is pivotally mounted so as to rotate about the axis
of the x-ray beam. This makes it possible to maintain the same
orientation for the image irrespective of the angular movements
about the Axes 3 and 4.
The equipment stand which has just been described can be associated
with elements which are employed in equipment stands of the prior
art. It is thus possible to associate a collimation 191 with the
x-ray source and an imaging chain 181 with the x-ray detector 12.
It is also possible to mount the x-ray source and the detector on
sliding devices 20 and 21 respectively so as to carry out their
relative displacement on the axis RX.
It is also possible to mount the x-ray source and the detector on
axes 22 and 23 respectively in order to operate with incident rays
on the detector or on an ancillary detector. It is also possible to
displace the Axis 2 vertically so as to obtain a variable position
of the isocenter in height.
FIG. 4 is a diagram in isometric perspective showing another
example of construction of an equipment stand in accordance with
the invention in which the pivot of the Axis 4 is located at ground
level and not in elevation as is the case with the equipment stand
of FIG. 3. Provision is accordingly made for an arm 17 which rests
and moves on the ground, thus avoiding the need to have a
cantilevered arm 17. In this figure, elements which are identical
with those of the previous figures are designated by the same
references.
FIG. 4 shows two positions of the equipment stand, namely one
position in which the isocenter 0 is located at the center on the
patient's head and the other position in which the isocenter 0 has
been brought to the level of the patient's lower limbs. This figure
has the main advantage of showing that the equipment stand in
accordance with the invention makes it possible to obtain a scan of
the isocenter 0 over a patient's entire body without having to
displace the examination table. It also shows that this equipment
stand permits freedom of access to the patient's head or to one of
the longitudinal sides according to the operator's requirements.
This results in reduced bulk of the x-ray installation while
providing greater flexiblity of use of the equipment stand.
More precisely, the equipment stand of FIG. 4 differs from that of
FIG. 3 in regard to the manner in which the rigid structure 17 is
constructed. The arcuate structure 17 has been replaced by an
equivalent structure having a horizontal portion 24 which rests on
the ground and moves in rotation on this latter by pivoting about
the Axis 3. That end of said horizontal portion 24 which is
opposite to the end of the Axis 3 supports a vertical portion 25
mounted for pivotal motion about the Axis 4 which is in rigidly
fixed relation to the horizontal portion 24. This vertical portion
25 in turn supports the arcuate member 13 and its associated
rotation means.
The invention has been described in connection with particular
examples of construction but may clearly be carried out in
different ways without thereby departing from its scope as defined
by the appended claims:
* * * * *